Strategies for treating infectious disease often focus on ways to enhance immunity. For instance, the most common method for treating viral infection involves prophylactic vaccines that induce immune-based memory responses. Another method for treating viral infection includes passive immunization via immunoglobulin therapy (Meissner, J. Pediatr. 124:S17–21, 1994). Administration of Interferon alpha (IFN-α) is another method for treating viral infections such as genital warts (Reichman et al., Ann. Intern. Med. 108:675–9, 1988) and chronic viral infections like hepatitis C virus (HCV) (Davis et al., New Engl. J. Med. 339:1493–9, 1998) and hepatitis B virus (HBV). For instance, IFN-α and IFN-β are critical for inhibiting virus replication (reviewed by Vilcek et al., (Eds.), Interferons and other cytokines. In Fields Fundamental Virology., 3rd ed., Lippincott-Raven Publishers Philadelphia, Pa., 1996, pages 341–365). In response to viral infection, CD4+ T cells become activated and initiate a T-helper type I (TH1) response and the subsequent cascade required for cell-mediated immunity. That is, following their expansion by specific growth factors like the cytokine IL-2, T-helper cells stimulate antigen-specific CD8+ T-cells, macrophages, and NK cells to kill virally infected host cells. Although oftentimes efficacious, these methods have limitations in clinical use. For instance, many viral infections are not amenable to vaccine development, nor are they treatable with antibodies alone. In addition, IFN's are not extremely effective and they can cause significant toxicities; thus, there is a need for improved therapies.
Not all viruses and viral diseases are treated identically because factors, such as whether an infection is acute or chronic and the patient's underlying health, influence the type of treatment that is recommended. Generally, treatment of acute infections in immunocompetent patients should reduce the disease's severity, decrease complications, and decrease the rate of transmission. Safety, cost, and convenience are essential considerations in recommending an acute antiviral agent. Treatments for chronic infections should prevent viral damage to organs such as liver, lungs, heart, central nervous system, and gastrointestinal system, making efficacy the primary consideration.
Chronic hepatitis is one of the most common and severe viral infections of humans worldwide belonging to the Hepadnaviridae family of viruses. Infected individuals are at high risk for developing liver cirrhosis, and eventually, hepatic cancer. Chronic hepatitis is characterized as an inflammatory liver disease continuing for at least six months without improvement. The majority of patients suffering from chronic hepatitis are infected with either chronic HBV, HCV or are suffering from autoimmune disease. The prevalence of HCV infection in the general population exceeds 1% in the United States, Japan, China and Southeast Asia.
Chronic HCV can progress to cirrhosis and extensive necrosis of the liver. Although chronic HCV is often associated with deposition of type I collagen leading to hepatic fibrosis, the mechanisms of fibrogenesis remain unknown. Liver (hepatic) fibrosis occurs as a part of the wound-healing response to chronic liver injury. Fibrosis occurs as a complication of haemochromatosis, Wilson's disease, alcoholism, schistosomiasis, viral hepatitis, bile duct obstruction, toxin exposure, and metabolic disorders. This formation of scar tissue is believed to represent an attempt by the body to encapsulate the injured tissue. Liver fibrosis is characterized by the accumulation of extracellular matrix that can be distinguished qualitatively from that in normal liver. Left unchecked, hepatic fibrosis progresses to cirrhosis (defined by the presence of encapsulated nodules), liver failure, and death.
There are few effective treatments for hepatitis. For example, treatment of autoimmune chronic hepatitis is generally limited to immunosuppressive treatment with corticosteroids. For the treatment of HBV and HCV, the FDA has approved administration of recombinant IFN-α. However, IFN-α is associated with a number of dose-dependent adverse effects, including thrombocytopenia, leukopenia, bacterial infections, and influenza-like symptoms. Other agents used to treat chronic HBV or HCV include the nucleoside analog RIBAVIRIN™ and ursodeoxycholic acid; however, neither has been shown to be very effective. RIBAVIRIN™+IFN combination therapy for results in 47% rate of sustained viral clearance (Lanford, R. E. and Bigger, C. Virology 293: 1–9 (2002). (See Medicine, (D. C. Dale and D. D. Federman, eds.) (Scientific American, Inc., New York), 4:VIII:1–8 (1995)).
Respiratory syncytial virus is the major cause of pneumonia and bronchiolitis in infancy. RSV infects more than half of infants during their first year of exposure, and nearly all are infected after a second year. During seasonal epidemics most infants, children, and adults are at risk for infection or reinfection. Other groups at risk for serious RSV infections include premature infants, immune compromised children and adults, and the elderly. Symptoms of RSV infection range from a mild cold to severe bronchiolitis and pneumonia. Respiratory syncytial virus has also been associated with acute otitis media and RSV can be recovered from middle ear fluid. Herpes simplex virus-1 (HSV-1) and herpes simplex virus-2 (HSV-2) may be either lytic or latent, and are the causative agents in cold sores (HSV-1) and genital herpes, typically associated with lesions in the region of the eyes, mouth, and genitals (HSV-2). These viruses are a few examples of the many viruses that infect humans for which there are few adequate treatments available once infection has occurred.
The demonstrated activities of the IL-28 and IL-29 cytokine family provides methods for treating specific virual infections, in particular, liver specific viral infections. The activity of IL-28 and IL-29 also demonstrate that these cytokines provide methods for treating immunocompromised patients. The methods for these and other uses that should be apparent to those skilled in the art from the teachings herein.